1. Field of the Invention
The invention relates to a method for minimizing the load on an internal combustion engine during the starting thereof. More particularly, the invention relates to a method of reducing the drag attributed to a starter-alternator when an internal combustion engine is started.
2. Description of the Related Art
Typically, an internal combustion engine is started initially from an electrical potential. Because an internal combustion engine is often used with a motor vehicle, the electrical potential comes from a battery. The battery needs to be charged shortly after the internal combustion engine is started because much of the potential stored in the battery is consumed during the starting of the internal combustion engine.
To solve this problem, an alternator/generator is driven by the internal combustion engine. This alternator is used as a generator to generate electricity to charge the battery. Starting the alternator/generator at the time the internal combustion engine is starting creates an additional drag on the internal combustion engine. This drag is perceived by the operator of the internal combustion engine and is undesirable and so it is not done.
More recently, the functions of the starter and the alternator have been combined into a single starter-alternator. With these assemblies, the same device that is used to start the internal combustion engine is the same device that charges the battery once the internal combustion engine has been started. One problem with such devices is these starter-alternators put a drag on the internal combustion engine that is perceptible by the operator of the motor vehicle.
In order to crank the engine with the starter-alternator, its field coil windings are energized with full field current at the same time as its stator windings are energized. This produces the needed torque to start the internal combustion engine. As the engine starts with fuel and spark and accelerates to idle speed, the starter-alternator begins to generate electricity and charges the battery. This results in a significant extra load on the battery that aggravates the feel of the starting process. This is not a problem with traditional cranking motors and alternators where the alternators are energized only after achieving idle speed.
This problem has been addressed in some internal combustion engine systems by forcing the field current to rapidly decrease to zero soon after a successful engine crank has been accomplished. This is done by means of a half bridge on a field circuit. This scheme provides a good starting response. The drag on the engine from the alternator still exists, however, for a brief moment when the field current is high from the cranking event and in the early park of its rapid decent to zero current.